It has been discovered that glucagon can stimulate the conversion of D-glyceraldehyde and dihydroxyacetone to glucose in isolated fasted rat livers. The goal of this proposal is to determine the site and mechanism of the glucagon effect. A working hypothesis is that glucagon acts in such a way as to increase the flux of both substrates across triokinase reactions to form glyceraldehyde 3 phosphate and dihydroxyacetone phosphate, respectively. The problem will be studied using (1) isolated fasted livers perfused with the substrate (unlabeled or labeled with C14) in the absence or presence of glucagon, (2) a 27,500 x g cytoplasmic fraction made from them and (3) isolated rat liver cells. Measurements of various hepatic metabolites and of the C14 in them will be made in extracts of perfused livers in search of clues pointing to a site(s) of action. Measurements of the activities of various enzymes will be made in the cell free system preparations for the same purpose. The use of an isolated cell preparation will afford the opportunity to study the glucagon effect on D-glyceraldehyde metabolism in a homogenous population of hepatic parenchymal cells. The enzymes to be evaluated will be primarily triokinase and both NADH- and NADPH-linked glycerol dehydrogenases, which catalyze the formation of glycerol from D-glyceraldehyde. Other enzymes will be assayed as indicated.